Resumen de Shear strength of off-eutectic AuGe joints at high-temperature
Andreas Larsson, Torleif A. Tollefsen, Knut E. Aasmundtveit
High-temperature compatible devices of SiC have been demonstrated in recent years. Together with a high-temperature compatible die-attach, they can form a basis for future reliable high-temperature electronics. This article presents shear strength capacity of Au-rich off-eutectic AuGe die-attach at temperatures above the eutectic melting point. Metallized (Ni/Au) SiC dice were joined to metallized (Cu/Ni/Au) Si3N4 substrates with eutectic AuGe preforms. The joints demonstrated a significant shear strength capacity up to 410 °C (50 °C above the eutectic melting point). High-quality Au-rich off-eutectic AuGe joints, comprising a AuGe mixture with 8 ± 4 at.% Ge, were formed with a low bond line pressure (240 kPa). At room temperature the shear strength was measured to be approximately 140 MPa, falling to approximately 40 MPa at 410 °C. This demonstrates that off-eutectic joints might be considered for use at temperatures above the eutectic melting point. The fracture mode was mainly cohesive in the off-eutectic AuGe layer when tested at a temperature below the eutectic melting point. Above the eutectic melting point, the fracture mode was complex with signs of a partially melted off-eutectic AuGe compound. Within this compound, columnar structures of the primary α phase (Au) was surrounded by an apparently melted and solidified phase. In other regions, an adhesive fracture at the interface between a slightly off-eutectic compound and a GeNi layer was discovered. The microstructure was found to be inhomogeneous with large regional variations within joints. From almost pure Au, primary α phase with up to 2–3 at.% Ge, up to near eutectic AuGe regions with an overall composition of 20–30 at.% Ge. In general, Ge was segregated into explicit domains within a primary α phase.
